Laminated rare earth structure and method of making

ABSTRACT

A laminated structure having two or more layers, wherein at least one layer is a metal substrate and at least one other layer is a coating comprising at least one rare earth element. For structures having more than two layers, the coating and metal substrate layers alternate. In one embodiment of the invention, the structure is a two-layer laminate having a rare earth coating electrospark deposited onto a metal substrate. In another embodiment of the invention, the structure is a three-layer laminate having the rare earth coating electrospark deposited onto a first metal substrate and the coating subsequently bonded to a second metal substrate. The bonding of the coating to the second metal substrate may be accomplished by hot pressing, hot rolling, high deformation rate processing, or combinations thereof. The laminated structure may be used in nuclear components where reactivity control or neutron absorption is desired and in non-nuclear applications such as magnetic and superconducting films.

[0001] This invention was made with Government support under ContractDE-AC0676RLO1830 awarded by the U.S. Department of Energy. TheGovernment has certain rights in the invention.

FIELD OF THE INVENTION

[0002] This invention relates generally to a laminated article ofmanufacture and a method of making wherein at least one layer of thelaminate comprises at least one rare earth element. More particularly,this invention relates to electrospark depositing a rare earth coatingon a metal substrate wherein the coating may be subsequently bonded toanother metal substrate. Still more particularly, this invention relatesto electrospark depositing the rare earth element erbium on a zirconiumalloy substrate that can be subsequently formed into a fuel assemblycomponent for neutronic control in a light water reactor. “Laminated”herein is defined as composed of layers of metallurgically-bondedmaterial with at least one substrate layer and at least one coatinglayer. “Rare earth” element is defined in the conventional manner, thatis, an element of the lanthanide series.

BACKGROUND OF THE INVENTION

[0003] The operation of a nuclear power plant requires that the reactorcore maintain criticality throughout the duration of its operatingcycle. In order to operate for an extended period of time, the reactorcore must initially have excess reactivity (i.e., an excess amount offissile material). This excess reactivity changes over time such that bythe end of its operating cycle, the excess reactivity approaches zero,and the reactor core can no longer remain critical. At this point, thereactor is shut down and the core is refueled.

[0004] The amount of excess reactivity in a reactor core is limited tomaintain a safe, controlled nuclear chain reaction. The primary methodof reactivity control is to fuel the reactor core with a number of fuel“batches”, each batch generally having been operated a cycle more thanthe succeeding batch. Ideally, the reactivity of each batch would bedesigned such that the average of the whole core allows the core to bejust critical. When a particular fuel batch does not have sufficientreactivity to meaningfully contribute to the excess reactivity ofanother fuel cycle, the batch is discharged to the spent fuel pool and afresh fuel batch takes its place.

[0005] Because fresh fuel must typically last for ˜1200-2000 effectivefull power days in the reactor (depending on the particular cycledesign), fresh fuel must be loaded with far more reactivity than wouldbe required if the fresh fuel only needed to last for 1 cycle. Thesehigh levels of excess reactivity require design measures to maintain thereactor core within acceptable safety margins. One of these designmeasures is the incorporation of a burnable neutron absorption material(sometimes called “burnable poison,” referred to hereinafter as simply“absorber”) within the fuel assemblies that provide “negative”reactivity to the batch in an amount that is able to help control theexcess reactivity as the reactor cycle proceeds (U.S. Pat No. 5,241,571,U.S. Pat. No. 5,267,290, and U.S. Pat. No. 5,872,826, referred tohereinafter as patents '571, '290, and '826, respectively).

[0006] Absorbers typically comprise one or more of the following highneutron absorption cross-section elements: boron, cadmium, silver,indium, hafnium, and the rare earth elements of gadolinium, erbium, andsamarium. Some of these absorbers have been incorporated in “discrete”absorber pins that occupy fuel pin lattice positions in a fuel assembly,as a coating on fuel pellets, as a constituent of the fuel, and as analloying element of a component of the fuel assembly (e.g., fuelcladding or structural members). All of these methods, however, haveshortcomings. For example, discrete absorber pins andabsorber-containing fuel displace power-producing fuel, operate at lowerlinear heat generation rates than standard fuel pins, and require morestringent controls in material handling and fabrication during fuelassembly manufacture. Furthermore, the alloying approach restricts therange of options available to the designer for choosing the optimumamount and spatial distribution of the absorber within the fuel assemblycomponent to meet reactivity needs.

[0007] A more attractive and versatile approach is provided by patent'826 which discloses a fuel assembly design comprising absorbers assheets that are embedded in the structural channel box of a fuelassembly using a variety of encapsulation, rolling, and pressingtechniques. Such an approach provides flexibility in the amount andlocation of the absorber within the fuel assembly and keeps the absorberfrom directly contacting the reactor coolant. In addition, this approachoffers a method to increase fuel burnup. By replacing theabsorber-containing structural member (e.g., guide tube, channel, duct)of a fuel assembly during a reactor shutdown with another membercontaining a lower amount of absorber (without replacing the fuel pins)and reinserting the assembly in the reactor, fuel lifetime can beincreased. The absorber sheets disclosed in patent '826 were made ofcadmium, samarium, boron, gadolinium, silver, indium and hafnium.

[0008] An optimum reactivity profile for each fuel assembly would be onethat has a flat reactivity curve throughout its life and then drops offto zero just prior to the assembly being discharged. Practically, thiswould require that the negative reactivity of the absorber in theassembly burn out at exactly the same rate as the fissile fuel, and thatall of the absorber is depleted at the end of the cycle. Any absorberthat remains at the end of the life of the fuel assembly contributes toa residual negative reactivity that can shorten assembly (and thereforecore) life. In practice, it is very difficult to achieve a flatreactivity curve with no absorber left at the end of assembly life. Eachabsorber has its own nuclear characteristics, and every reload batch isa compromise between competing alternatives.

[0009] In this regard, the designer has two considerations to achievethe compromise in designing a core load. First, any residual negativereactivity from absorber that remains at the end of assembly liferesults in a loss of economic value of the assembly. There is no way tomitigate the presence of residual negative reactivity except to add morefissile material to the initial fuel load. Clearly, the best designswould minimize residual negative reactivity. Second, the amount of fuelassembly excess reactivity controlled by the absorber during the life ofthe assembly may be highly variable. This is because there are a varietyof methods that can be used to control overall core reactivity,including control rods, water flow, etc. In addition, there is generallysufficient thermal margin in fuel designs to allow reasonably wideassembly power/reactivity swings (˜25%) through the life of theassembly. However, there are limits to what can be accommodated from asafety standpoint in a core design. It is clear, however, that it wouldbe more economically desirable to design an assembly that has largerswings in reactivity than a large amount of residual negativereactivity.

[0010]FIG. 1 provides a graphical comparison of some reactivitycalculations for several sample fuel assembly designs containing avariety of absorbers. The “Gadolinium Pins” curve is the baseline curverepresenting a fuel assembly designed with gadolinium mixed with fuel inseveral fuel pins in the assembly. This design represents the currentstate of the art of absorber application in boiling water reactors(BWRs). Fuel pins with gadolinium have been used for a number of years,and has provided a reasonable balance of reactivity and residualnegative reactivity. The other curves shown in FIG. 1 use an absorberincorporated in the structural member of the fuel assembly. As discussedpreviously, incorporation of the absorber in a structural member (as annon-alloying element) has advantages over other approaches.

[0011] The common basis for each curve in FIG. 1 is that each absorberanalyzed is placed in an assembly with the same initial amount of U-235.The amount of absorber is adjusted to try to obtain a reactivity curvethat is as constant as possible with a peak reactivity of <1.2 and aminimum reactivity >0.9. Therefore, the reactivity potential of each ofthe sample assemblies calculated is exactly the same. The figure clearlyshows the differences that can be achieved with the different absorbers.

[0012] The use of samarium, hafnium, indium or silver, as suggested bypatent '826, would not meet the economic requirements of a fuel assemblywith minimal residual reactivity. As can be seen in FIG. 1, samarium andsilver clearly result in a significant residual reactivity penalty ascompared to the baseline. Samarium also has the additional disadvantageof having a very large increase in reactivity at the beginning ofoperation, which could potentially result in operational difficulty inmaintaining safety margins. Hafnium and indium are much better for thisapplication, however, there is still a penalty relative to the baseline.The penalty would result in tens of days less operation, which would beassociated with a significant cost penalty. Given the penalty of usinghafnium or indium in comparison with the state of the art, there wouldbe little economic advantage to incorporating hafnium or indium in thechannel.

[0013] The incorporation of boron into the structural member, alsosuggested by patent '826, would be an adequate absorber from thestandpoint of residual reactivity worth. The residual reactivity at 2000days is quite similar to the baseline. However, the reactivityfluctuations are relatively large in the first 800 days. The largefluctuation may be difficult to accommodate safely during operations. Incomparison to the baseline, the use of boron would provide littleoperational advantage, and may make operations more difficult. Becauseof this, there would be no clear reason that the use of boron in thestructural member would be better than the state of the art.Furthermore, boron produces. helium as a result of neutron capture andmay result in degradation of the structural integrity of the assembly.

[0014] As shown in FIG. 1, the use of erbium (Er) results in arelatively smooth reactivity curve. The initial and peak reactivitiesare similar to the baseline, however the curve is much flatter than thebaseline through 800 days. This would likely result in fuel assemblydesigns that can maintain the safety and thermal margins that are in thecurrent gadolinium assemblies. The real reactivity benefit, however, canbe seen after 800 days when it becomes clear that the residual negativereactivity component is much less than the baseline. The cycle benefitmay be on the order of 150-200 days, which could be directly transferredinto fuel cycle savings either through a reduced initial enrichmentrequirement or through longer operating cycles. Depending on thespecific neutronic requirements, further benefits may be obtained bycombining the Er with other absorbers.

[0015] Support for the use of Er as the absorber is further provided bypatents '571 and '290. Patent '571 discloses Er as an alloying elementfor the zirconium-based fuel cladding or structural member of the fuelassembly. Patent '290 discloses a coextruded fuel pin cladding having alayer of zirconium absorber alloy containing Er. Despite these positivedevelopments in the use of Er, the approaches disclosed in patents '571and '290 still have some of the shortcomings discussed earlier. It is ofinterest that the more attractive and versatile approach ofincorporating the absorber as an embedded sheet in a structural member(patent '826) does not teach or even suggest the use of Er.

[0016] Accordingly, there is a continuing need to incorporate aneffective absorber, such as the rare earth element Er, in a structuralmember of the fuel assembly that overcomes the shortcomings of presentmethods and that improves the performance of fuel assemblies.

SUMMARY OF THE INVENTION

[0017] The present invention is a laminated article of manufacture and amethod of making. The article is a structure having two or more layers,wherein at least one layer is a metal substrate and at least one otherlayer is a coating comprising at least one rare earth element. Forstructures having more than two layers, the coating and metal substratelayers alternate. In the simplest embodiment of the invention, thestructure is a two-layer laminate consisting of a metal substrate (asthe first layer) and a coating (as the second layer) formed on the metalsubstrate. The coating is formed by electrospark depositing a materialon the metal substrate from an electrode comprising at least one rareearth element. In a slightly more complex embodiment of the invention,the structure is a three-layer laminate made from a two-layer laminateby the additional step of bonding a second metal substrate to thecoating layer. The substrates may be any metal though reactor-gradezirconium-based alloys, iron-based alloys, and nickel-based alloys arepreferred for in-reactor nuclear applications such as fuel assembly orfuel storage components. The bonding of the coating to the second metalsubstrate may be accomplished by hot pressing, hot rolling, highdeformation rate processing (e.g., explosive bonding), or combinationsthereof.

[0018] In view of the foregoing, it is an object of the presentinvention to bond at least one rare earth to a substrate that can besubsequently mechanically formed into a structure without flaws such aspores, cracks, or delaminations.

[0019] It is a further object of the present invention to form alaminate having a sandwiched rare earth layer that can subsequently becold worked or hot worked while maintaining structural integrity.

[0020] It is a further object of the present invention to form alaminate having a sandwiched rare earth layer wherein the rare earth isimmobile.

[0021] It is a further object of the present invention to form alow-cost, robust, and damage resistant laminate that is useful inapplications requiring rare earth films.

[0022] It is a further object of the present invention to electrosparkdeposit material comprising Er on a zirconium alloy substrate that canbe subsequently formed into a neutronic control structure for a lightwater reactor.

[0023] It is a further object of the present invention to increase theperformance of fuel pins while maintaining or increasing the margin ofsafety associated with corrosion of a fuel assembly comprising thestructure.

[0024] It is a further object of the present invention to increase theperformance of fuel pins while maintaining or increasing the margin ofsafety associated with the structural integrity of a fuel assembly.

[0025] It is a further object of the present invention to decrease thehandling and material control requirements during fuel assemblyfabrication.

[0026] The subject matter of the present invention is particularlypointed out and distinctly claimed in the concluding portion of thisspecification. However, both the organization and method of operation,together with further advantages and objects thereof, may best beunderstood by reference to the following description taken in connectionwith accompanying drawings wherein like reference characters refer tolike elements.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]FIG. 1 is a graph comparing the predicted in-reactor performanceof various absorbers;

[0028]FIG. 2a is an illustration of the first embodiment of theinvention;

[0029]FIG. 2b is an illustration of the second embodiment of theinvention;

[0030]FIG. 2c is an illustration of the third embodiment of theinvention;

[0031]FIG. 3a is an optical micrograph (400×) of Er foil hot pressedbetween two Zr-4 sheets at 800° C. and 34.5 MPa for 4 Hours;

[0032]FIG. 3b is a macro photograph of a Zr-4/Er/Zr-4 laminate thatfailed during subsequent cold rolling;

[0033]FIG. 3c is an optical micrograph (200×) of a Zr-4/Er/Zr-4 laminatethat failed during subsequent cold rolling;

[0034]FIG. 3d is an optical micrograph (200×) of a Zr-4/Er/Zr-4 laminatethat failed during subsequent hot rolling;

[0035]FIG. 4a is a scanning electron micrograph of anelectrospark-deposited Er coating with a nominal thickness of 55 μm;

[0036]FIG. 4b is a composition profile of the electrospark-deposited Ercoating shown in FIG. 4a:

[0037]FIG. 4c is a hardness (Vickers microhardness, 10 g load) profilefor the Er coating shown in FIG. 4a;

[0038]FIG. 5a is a scanning electron micrograph of a Zr-overcoated Ercoating with a nominal thickness of 17 μm;

[0039]FIG. 5b is a composition profile of the Zr-overcoated Er coatingshown in FIG. 5a;

[0040]FIG. 6 is an optical micrograph (200×) of a laminate produced byhot roll bonding after TIG welding under He; and

[0041]FIG. 7 is an optical micrograph (220×) of a laminate produced byhot roll bonding after EB welding under vacuum.

DETAILED DESCRIPTION OF THE INVENTION

[0042] The present invention is a laminated article of manufacture and amethod of making. The article is a structure having two or more layers,wherein at least one layer is a metal substrate and at least one otherlayer is a coating comprising at least one rare earth element. Forstructures having more than two layers, the coating and metal substratelayers alternate. The structure would be useful in in-core orout-of-core nuclear components where reactivity control or neutronabsorption is desired. In-core components include, but are not limitedto, guide tubes/thimbles in pressurized water reactors (PWRs) andchannels in BWRs. Out-of-core or out-of-reactor components include, butare not limited to, fissile material storage components such as fissilefeedstock containers, green/spent fuel storage racks or fixtures, andgreen/spent fuel assembly transportation and storage canisters/casks.The structure would also be useful in non-nuclear applications thatexploit the special chemical and physical properties of the rare earths(e.g., magnetic and superconducting films).

[0043] Though the following three embodiments illustrate a laminate ofup to 5 layers, the present invention is not limited to these numbers oflayers or these combinations of layer compositions: It will be apparentto those skilled in the art, that other numbers of layers and othercombinations of layer compositions may be required to meet certainnuclear or other operational requirements of a specific rare earthapplication.

[0044] In the first embodiment of the invention, shown in FIG. 2a, thestructure 10 is a two-layer laminate consisting of a coating 20 on afirst metal substrate 30′. The coating 2 is formed by the process ofelectrospark-depositing a first material on the first metal substrate30′ from a first electrode comprising at least one rare earth element,preferably containing Er for neutronic control applications. It ispreferred that the electrospark deposition comprises the step ofrotating the first electrode while rastering the first electrode acrossthe first metal substrate 30′ while depositing the first material fromthe first electrode onto the first metal substrate 30′ through theplasma arc. Rastering of the first electrode over the first metalsubstrate 30′ provides efficient and thorough electrospark-depositing ofthe coating 20 in a single pass. Rotating, oscillating, or vibrating thefirst electrode helps prevent the electrode from welding itself to thesurface. Depending on the specific application, the electrode maycomprise a combination of rare earth elements (e.g., Er and Gd forneutronic applications). As known to those skilled in the art, therequired percentage of rare earths in the electrode will depend on thedesired deposition amount in the specific application. As also known tothose skilled in the art, fewer electrospark deposit passes will berequired to deposit a given amount of rare earth the higher rare earthcontent in the electrode.

[0045] The first metal substrate 30′ may be any conductive metal. Innuclear applications, it is preferred that the first metal substrate 30′is selected from the group of nuclear-grade zirconium-based alloys,iron-based alloys, and nickel-based alloys. For light water reactorapplications (e.g., component in a fuel assembly), it is preferred thatthe first metal substrate 30′ is selected from the group ofreactor-grade zirconium alloys including Zr—Sn alloys (e.g., UNS alloysR60802 [Zircaloy-2] and R60804 [Zircaloy-4]), Zr—Nb alloys (e.g.,R60901), derivatives thereof, or combinations thereof (i.e., Zr—Sn—Nballoys). This embodiment would be useful in applications whereby it isacceptable to expose the coating 20 to the environment (e.g., in somefissile material storage applications).

[0046] In the second embodiment of the invention, shown in FIG. 2b, thestructure 10 builds upon the two-layer embodiment shown in FIG. 2a bythe addition of another layer. The laminate consists of the coating 20on a first metal substrate 30′ with a second metal substrate 30″ bondedto the coating 20 Like the first metal substrate 30′, the second metalsubstrate 30″ may be any conductive metal. In nuclear applications, itis preferred that the second metal substrate 30″ is selected from thegroup of nuclear-grade zirconium-based alloys, iron-based alloys, andnickel-based alloys. For light water reactor applications (e.g.,component in a fuel assembly), it is preferred that the second metalsubstrate 30″ is selected from the group of reactor-grade zirconiumalloys including Zr—Sn alloys (e.g., UNS alloys R60802 and R60804),Zr—Nb alloys (e.g., R60901), derivatives thereof, or combinationsthereof (i.e., Zr—Sn—Nb alloys). In this embodiment, the secondsubstrate 30″ may be made out of the same, or different, material asthat of the first substrate 30′. Furthermore, the coating 20 may also beformed by the process of electrospark-depositing a first material ontothe first metal substrate 30′ from a first electrode comprising a rareearth and then electrospark-depositing a second material into the firstmaterial from a second electrode comprising another element such asanother rare earth, an absorber, or a second metal substrate 30″ baseelement (e.g., Zr, Fe, or Ni). It is intended that such an addition of asecond material enhances certain properties of the resultant coating 20over the first material (e.g., to facilitate bonding of the coating 20to the second metal substrate 30″ or to further improve neutronicperformance). The bonding of the coating 20 to the second metalsubstrate 30″ may be accomplished by hot pressing, hot rolling, cold orhot high deformation rate processing (e.g., explosive bonding), orcombinations thereof.

[0047] The second embodiment would be useful in applications whereby itis advantageous for the coating 20 not to be exposed to the environment(e.g., as a fuel assembly component). An attractive feature of theembodiment of FIG. 2b is that if the first metal substrate 30′ andsecond metal substrate 30″ represent materials already certified for aspecific environment (e.g., a light water reactor), the structure 10does not introduce new materials directly to the environment that couldpose corrosion, pressure drop, and other safety-related problems. Mostimportantly, the structure 10, as shown in FIG. 2b, has high structuralintegrity. No significant flaws are introduced in the coating 20 and therare earth, absorber, or second metal substrate 30″ base element isimmobile within the structure 10. There is also a significant costsavings in minimizing the amount of qualification and certification ofsuch a new structure 10 for nuclear use. Furthermore, if the coating 20could be incorporated early in the fuel assembly manufacturing process,fabrication of assemblies potentially could proceed with minoradditional considerations (e.g. welds and heat affected zones,non-destructive evaluation for absorber assay).

[0048] The third embodiment of the invention, shown in FIG. 2c, providesan example of one of the numerous combinations of metal substrates andcoatings that builds upon the second embodiment of FIG. 2b. In thisembodiment, the structure 10 is a five-layer laminate consisting offirst and second metal substrates 30′, 30″ and three coatings 20, 20′,and 20″. The coatings 20′ and 20″ have the same compositional limits asthe coating 20 of the first two embodiments and are formed on therespective metal substrates in the same manner as the coating 20 in thefirst two embodiments.

EXAMPLE 1

[0049] Example 1 herein illustrates the failure of the prior art whichthe present invention is intended to improve. As described below,attempts were made to form a laminate, without electrospark deposition,using Er foil sandwiched between two Zircaloy-4 (Zr-4) sheets, similarto the approach of patent ′826. This approach proved unsuccessful andhighlighted the need for a new and different approach (provided hereinas the present invention, exemplified by Example 2 below).

[0050] The Er foils were 0.01 cm thick and 5 cm square, with a reportedpurity of 99.9%. The fully-annealed Zr-4 sheets had a nominal thicknessof 0.25 cm, a width of 20 cm and a length of 244 cm. The chemistry ofthe Zr-4 sheet was within the specification limits as described in ASTMStandard B 352-79.

[0051] Prior to fabricating the laminates, the Zr-4 sheet was shearedinto substrates approximately 5 cm square. The Er foils were packed andshipped from the supplier under inert gas. They were removed from thepackaging immediately prior to lamination to minimize oxidation. Some ofthe Er foils were cut into four smaller pieces, approximately 2.5 cmsquare, while other laminates were fabricated with full 5 cm squarefoils.

[0052] Initial attempts at cold roll bonding Zr-4/Er/Zr-4 laminates wereunsuccessful. Hot roll bonding initially was not attempted due toconcerns over the reactivity of the Er foil at high temperatures.Therefore, vacuum hot pressing was adopted as a means to simulate hotroll bonding, so that the mechanical forming characteristics of thelaminates could be studied. This approach allowed an evaluation of thepotential for fabricating and forming Zr-4/Er/Zr-4 laminates without theneed for elaborate encapsulation or roll bonding development. A set offabrication parameters was developed by hot pressing sheets of Zr-4together until acceptable joints were produced. These parameters werethen applied to the fabrication of hot-pressed laminates consisting ofEr foil sandwiched between two Zr-4 sheets.

[0053] The Zr-4/Er/Zr-4 laminates were produced by hot pressing invacuum at a temperature of 800° C. Applied pressures ranged from 34.5 to48.3 MPa and pressing times ranged from 4 to 5 hours. Some of theresulting laminates were sectioned for metallography, while others wereset aside for subsequent mechanical forming typically used to producestructural members (e.g., cold and/or hot rolling for BWR channelboxes). Subsequent cold or hot rolling was conducted at room temperature(RT) or 800° C. to an overall thickness reduction of 20%. Opticalmetallography was performed on sections of as-rolled laminates.

[0054]FIG. 3a shows a typical Zr-4/Er/Zr-4 laminate. The laminate waspressed at 800° C. and 34.5 MPa for 4 hours. There is some evidence ofsolid-state diffusion into the Er foil, forming an unidentifiedgray-colored phase on the Er side of the Zr-4/Er interfaces. The bondbetween the Er and Zr-4 appears good, with no cracks or porosityapparent.

[0055]FIG. 3b shows a laminate pressed under the same conditions as thesample shown in FIG. 3a that was then subjected to cold rolling with 20%overall reduction. The Er foil in this sample was 5 cm square, andextended to the edge of the Zr-4 sheets. The laminate split open as itexited the rollers. Close examination of the fracture surface revealedthat the laminate failed within the Er, and not at one of the Er/Zr-4interfaces.

[0056]FIG. 3c shows a laminate fabricated by hot pressing at 800° C. and48.3 MPa for 5 hours that was then subjected to cold rolling with 20%overall reduction. Note the cracks near the center of the Er foil.Although these did not appear to extend the entire length of the sample,there were regions that were heavily cracked. This particular sample hada 2.5 cm square piece of Er foil. This sample did not delaminate afterrolling, the Zr-4 surrounding the Er probably arresting the cracks andpreventing delamination. By comparing thicknesses measured frommicrographs of as-pressed and as-rolled samples, the reduction in Erthickness during cold rolling was consistently between 30% and 40%.

[0057]FIG. 3d shows a laminate fabricated by hot pressing at 800° C. and48.3 MPa for 5 hours that was then subjected to hot rolling at 800° C.to 20% overall reduction. Like the sample in FIG. 3c, this sample wasfabricated with a 2.5 cm square piece of Er foil sandwiched between two5 cm square sheets of Zr-4. Cracks are apparent near the center of theEr foil, although they are not quite as extensive as those inducedduring cold rolling (FIG. 3c). However, the estimated Er thicknessreduction in the hot-rolled sample is between 35% and 40%, which iscomparable to the reduction observed in the cold rolled samples.

[0058] The results of Example 1 can be explained by reviewing themechanical properties of Er and Zr-4. The mill certification for theZr-4 sheet listed its yield strength in the longitudinal direction as390 MPa and 151 MPa at room temperature (RT) and 288° C., respectively.The reported elongation of the Zr-4 sheet in the longitudinal directionwas 29% and 49% at RT and 288° C., respectively. Literature data on thestrength and ductility of Er metal are scarce, but most of the availablesources appear to agree with one another reasonably well. Gschneidnerreports (Gschneidner, K A. 1961. Rare Earth Alloys. Princeton, N.J.: D.van Nostrand Company, Inc.) the yield strength of cast Er to be 291 MPa,204 MPa, and 198 MPa at RT, 205° C., and 425° C., respectively. Theelongation of cast Er is reported to be 4.0%, 5.5%, and 6.8% at RT, 205°C., and 425° C. respectively. Gschneidner also reports the yieldstrength of forged Er to be 292 MPa, 316 MPa, and 131 MPa at RT, 205°C., and 425° C., respectively. The elongation of forged Er is reportedto be 7.0%, 4.6%, and 4.6% at RT, 205° C., and 425° C., respectively.Love and Kirkpatrick report (Love, B. and C. Kirkpatrick. 1961.“Mechanical Properties of Rare Earth Metals,” in Rare Earth Research,Ed. E. V. Kleber, New York, N.Y.: The Macmillan Company) the yieldstrength of cast Er to be 267 MPa, 239 MPa, and 173 MPa at RT, 204° C.,and 427° C., respectively. They report the elongation of cast Er to be4.0%, 5.5% and 6.7% at RT, 204° C. and 427° C., respectively. Theseauthors also report the yield strength of wrought (swaged) Er coldworked and hot worked from 20% to 68% reduction in area. The RT yieldstrength of these samples ranged from 231 MPa to 348 MPa, with RTelongation ranging from 1% to 6%.

[0059] From the foregoing, the yield strength of Zr-4 is approximately38% higher than either cast or forged Er at room temperature. Thisdifference probably explains the difference between the 20% overall coldwork in the cold rolled laminates and the 30% to 40% cold work observedin the Er foil itself. Also, the elongation of Zr-4 is 4 to 7 timesgreater than Er metal at room temperature. This difference explains thepresence of the cracks in the Er foil, since the material could notaccommodate the observed 30% to 40% thickness reduction without failing.No literature data are available for the mechanical properties of Er at800° C., but based on the metallographic results, it appears similararguments could be made at these temperatures. Based on the observed 35%to 40% reduction in thickness during hot rolling, it appears thedifferential strength between Zr-4 and Er is comparable at 800° C. andRT. The fact that fewer cracks are observed at 800° C. may indicate thatthe ductility of Er at these temperatures is improved, although notenough to accommodate the measured reduction in thickness.

[0060] Based on these results, it appeared that laminates of Er and Zr-4(and other zirconium-based alloys such as Zircaloy-2) could besuccessfully fabricated by hot pressing, however, these laminates couldnot subsequently be cold rolled or hot rolled to an overall thicknessreduction of 20% due to failures in the Er. Further, it was unlikelythat hot roll bonding would successfully produce a well-bonded andundamaged laminate using Er foil. The cause of the failures appears tobe the difference in strength and ductility between the Zr-4 sheet andthe Er metal. Therefore, it appeared that this approach to producingZr-4/Er/Zr-4 laminates for structural members in fuel assemblies was notfeasible (and possibly why patent ′826 did not disclose Er as acandidate material for that application).

EXAMPLE 2

[0061] The creation of a Zr-4/Er/Zr-4 laminate that could sustainsubsequent mechanical working without inducing flaws, such as cracks ordelaminations, proved to be a challenging fabrication task. Asillustrated in Example 1, the wide disparity in mechanical propertiesbetween the zirconium (Zr) alloy and Er foil resulted in laminarcracking and separation in the Er layer. Consequently, various coatingprocesses were considered as a first step in forming a laminate,especially those processes that could form a strong metallurgical bondbetween the coating and substrate. It was believed that by firstlayering Er on a substrate and then sandwiching the Er layer betweenanother substrate, a satisfactory laminate could be formed. Coatingprocesses such as thermal spray processes (e.g., plasma spray) andvacuum processes (e.g. sputtering, electron beam evaporation, ioncoating) were considered as a first step in forming but were expected tobe unacceptable due to being expensive or impractical for the geometriesof substrates expected, or not providing an Er layer that would maintainintegrity throughout its thickness during subsequent mechanical working.Laser cladding by rastering a laser over the surface of an Er powderdispersed on a Zr-4 substrate was also considered due to the strongmetallurgical bonds it can create. The high capital equipment expense,however, prevented development of this technique.

[0062] Based on electrospark-deposition (ESD) effectively andeconomically creating extremely hard, robust, and galling-resistantcoatings for reactor components (U.S. Pat. No. 4,649,086), this coatingtechnique was selected as a candidate for producing a satisfactoryZr-4/Er/Zr-4 laminate. The ESD process (Johnson R N, “Principles andApplications of Electro-Spark Deposition,” Proceedings of the 1_(st)International Conference on Surface Modification Technology, Phoenix,Ariz., Jan. 25-28, 1988) uses very short duration (i.e., a fewmicroseconds) pulses to remove material from a metallic or cermetelectrode in a plasma arc and to deposit it on a conductive metallic orcermet substrate. The time between pulses is on the order of amillisecond, which allows a relatively long cooling time between pulsesand results in rapid solidification of the deposit and low heat input tothe substrate. The rapid solidification typically produces exceptionallyfine-grained or nano-structured deposits that exhibit unusually goodwear and corrosion properties.

[0063] The ESD process creates some of the most robust anddamage-resistant coatings known. Advantages include the ability toproduce highly robust coatings with little heat input and without theuse of expensive vacuum chambers or sound-control booths. The process isenvironmentally benign in that it produces no hazardous wastes, fumes,or effluents. Capital equipment costs are low, and the process isportable for use in the field, lab, shop, or production floor. ESD,however, does involve a large number of process parameters that must becontrolled for consistent performance.

[0064] The ESD process lends itself well to automation and controlledplacement. Further, the technique can be easily adapted to providecoatings of different compositions or thicknesses at different locationson the substrate material. This could provide a significant neutronicperformance advantage by tailoring the amount of absorber material atdifferent radial and/or axial positions in the reactor core to optimizethe flux profile.

[0065] Two significant modifications to traditional ESD coating weredeveloped to produce satisfactory Er coatings on Zr-4. The first wasadapting the technique to use square cross-section electrodes becausethe supplier of the Er rods was unable to produce a round cross-sectionrod with the desired dimensions. The second modification was adaptingthe technique to produce coatings under an inert cover gas rather thanin air. As discussed previously, ESD is essentially a type of pulsed arcwelding, and relatively high temperatures are reached when the arc isrepeatedly struck between the electrode and the substrate. Metallographyof Er coatings produced in air suggested that significant oxidationoccurred in the highly reactive Er, which led to embrittlement andcracking upon cooling. With an inert cover gas, Er coatings up to 75 μmthick were successfully produced in a single pass. Metallography ofthese coatings revealed excellent coverage with no cracks, gooduniformity in thickness, and a relatively smooth surface. Thickercoatings were produced by producing Er layers in successive passes.Coatings up to 150 μm thick, produced in 3 passes, were successfullyfabricated. Like the single pass coatings, the multiple pass coatingshad no cracks, and exhibited acceptable uniformity, surface roughness,and layer-to-layer bonding. The combined deposition rate, thickness, anduniformity associated with these Er coatings have never been achievedwith any other material; typical ESD coatings are deposited at about 10μm per pass and many coatings crack at thicknesses greater than about 25μm.

[0066] ESD operating parameters that are important to achievingacceptable coatings include spark energy, duration, voltage, current,capacitance, frequency, environment, substrate temperature, contactpressure, electrode speed relative to the substrate, electrode motion,geometry of electrode contact, and substrate and electrode composition.Several combinations of parameters were found that achieved acceptablecoatings at a rate of about 5 mg/min (˜5 microns thickness at a coveragerate of 1 cm²/min). Thicker coatings were produced through multiplepasses. However, by continued experimentation with process parameters, aset of conditions that produced more than an order of magnitude increasein deposition rates was unexpectedly found. Er coatings of 75 micronsthick on Zr-4 substrates were produced in each pass, for a depositionrate of about 70 mg/min. The specific ESD operating parameters forproducing Er coatings included careful control of the argon gasenvironment and are listed below in Table 1. TABLE 1 DepositionParameters for Applying Erbium Using ESD Spark Duration: 5 to 50microseconds (this is a characteristic of the power supply used)Voltage: 50 to 200 volts (160 volts is preferred for high depositionrates) Current: 1.5 to 8 amps (3 amps is preferred) Capacitance: 10 to60 mfd (40 mfd is preferred) Frequency: 100 to 1500 Hz (500 Hz ispreferred) Environment: Any inert gas (Argon is preferred because it isinexpensive and ionizes well) Substrate Temperature: RT to 200° C. (RTis preferred) Electrode/Substrate 5 to 125 gram force (30 gram force ispreferred) Contact Pressure: Electrode Speed 0.25 to 5 cm per second(1.25 cm per second is Relative to Substrate: preferred) ElectrodeMotion: Rotating, oscillating, or vibrating (rotating at 200 rpm ispreferred) Geometry of Electrode Perpendicular to substrate surface to15 degrees Contact: from perpendicular (7 degrees from perpendicular ispreferred) Substrate composition: Any metal (zirconium alloy ispreferred, Zr-4 is most preferred) Electrode composition: Er/Zr alloy(pure Er is preferred) Step-over distance .05 to .5 mm (.05-.08 mm ispreferred) (distance moved after 1 traverse with the electrode to layanother bead next to the 1^(st) bead):

[0067] The electrodes used for ESD were Er rods nominally 0.32 cm squareand 15 cm long, with a reported purity of 99.9%. Rod density in thefirst batch ranged from 88.8% to 91.2% of theoretical (9.05 g/cm³). Thesecond batch ranged from 88.3% to 93.5% of theoretical density.

[0068] A variety of Er coatings were first applied to Zr-4 sheetsapproximately 5 cm square. Furthermore, some of these Er coatings weresubsequently coated with Zr (i.e., a Zr “overcoat”) to investigatewhether this dual coating composition would improve the structuralintegrity of the later-formed laminate. The Zr electrodes used forovercoating were fabricated from 1 mm diameter annealed Zr wire having99.2% purity.

[0069]FIG. 4a depicts a typical ESD Er coating with a nominal thicknessof approximately 55 μm. The image in FIG. 4a was obtained with ascanning electron microscope in back-scattered electron mode tohighlight composition contrast. Note the sharp coating/substrateinterface and the relative uniformity of the coating composition. Thereis some contrast at the surface of the coating that may be an oxide filmproduced during or after coating. Also visible in FIG. 4a are severalVickers microhardness indentations. Note that except for the one closestto the coating surface, there is no evidence of cracks emanating fromthe indentations, suggesting a degree of toughness in the coating. Thebrittle nature of the indentation nearest the surface probably can beattributed to a surface effect or an oxide film. The porous areas in thecoating are most likely the result of inhomogeneities in the Er rodsused as ESD electrodes. FIG. 4b shows Zr, Sn and Er energy dispersivex-ray spectroscopic (EDS) composition profiles across the thickness ofthe coating depicted in FIG. 4a. Note the steep compositional gradientsat the coating/substrate interface and the relative uniformity of thecoating composition (Er with approximately 5 a/o Zr). Interestingly,this coating composition was found to be common to all the Er coatingsindependent of their thickness or process parameters. FIG. 4c shows theVickers microhardness profile corresponding to the indentations in FIG.4a. The hardness across most of the coating thickness is equal to, orgreater than, the hardness of the zircaloy substrate. This suggests theultimate tensile strength of the coating is comparable to, or greaterthan, the strength of the substrate, which bodes well for subsequentmechanical processing.

[0070]FIG. 5a shows a typical ESD Zr-overcoated Er coating with anominal thickness of approximately 17 μm. As with the Er coating shownin FIG. 4a, there is a sharp coating/substrate interface and relativelyuniform composition throughout the coating (as indicated by the lack ofvisual contrast in the back-scattered electron image shown in FIG. 5a).Also, the surface appears relatively free of distinct phases (i.e. oxidefilms). FIG. 5b depicts an ESD composition profile across the thicknessof the coating in FIG. 5a. In general, it is very similar to the profileshown in FIG. 4b for the Er coating, in that it has a steepcompositional gradient at the coating/substrate interface and arelatively constant composition across the thickness of the coating.However, the Zr content of the coating is approximately 25 a/o in thiscase due to the Zr overcoat at the Er surface (the dual Zr contentgradient is apparent from the minimum in Zr concentration shown in FIG.5b). As with the Er coatings, the Zr content of the coating isessentially independent of Er or Zr overcoat thickness and processparameters.

[0071] The Zr—Er phase diagram suggests that both the Er and theZr-overcoated coatings should exist as a two-phase mixture of α-Zr andEr. The microstructural evidence suggests that this mixture is uniformlydistributed and of relatively fine scale. The insensitivity of thecoating composition profiles to thickness and process parameterssuggests these coatings would lend themselves to good process controland repeatability in a commercial setting. Further, the ability totailor the Er concentration by Zr overcoating or by using a Zr—Er alloyelectrode appears to offer the promise of precise incorporation of thedesired amounts of rare earth in the final product. Coupled with theinherent capability of the ESD technique to accurately place the coatingmaterial on the zircaloy substrate, it appears this approach offers avery flexible method for incorporating the desired amount of rare earthin exactly the desired locations.

[0072] Laminates having 3-layers were formed by pairing Er-coated,Zr-overcoated Er, or uncoated (“bare”) Zr-4 substrates with Er-coated orZr-overcoated Er substrates such that the coatings formed the innerlayer and the substrates formed the outer layers of the laminate. Priorto this layering in preparation for bonding, any bare Zr-4 surface to bebonded was sanded with 400 grit SiC paper (grit blasting would also beacceptable). All surfaces to be bonded were then swabbed with B-etchsolution for several minutes to remove any oxide film and rinsed withwater to remove any residual solution. After surface preparation, thelaminates were rapidly transported to an inert gas or vacuum environmentto prevent oxide formation on the surfaces to be bonded. To preventoxide formation during the bonding process, the laminates wereseal-welded along the periphery of the laminates using either thetungsten inert gas (TIG) method under He or the electron beam (EB)method under vacuum. The laminates were then subjected to hot rollbonding in air to simulate the expected mechanical processing requiredin a commercial manufacturing operation.

[0073] Laminates were hot roll bonded at 800° C. at overall thicknessreductions of 10% to 20%. The bonded laminates were subsequentlyannealed in air at 800° C. for at least 30 minutes to relieve theinduced stresses and to recrystallize the Zr-4. The best results wereobtained with either Er or Zr-overcoated Er laminates bonded withuncoated Zr-4 substrates. FIG. 6 shows a bonded Zr-4/Er/Zr-4 laminatemade by TIG seal welding and then hot roll bonding an Er-coatedsubstrate to an uncoated Zr-4 substrate. Similar results were obtainedby hot roll bonding a Zr-overcoated Er-coated coupon with an uncoatedZr-4 substrate. Attempts to hot roll bond two Er-coated and twoZr-overcoated Er-coated laminates to each other were unsuccessful. Thelack of bonding was presumably related to the presence of an oxide filmon the coated surfaces.

[0074] TIG seal welding of the laminates under He prior to hot rollbonding, however, prevented complete bonding during hot rolling. Abetter seal welding/bonding technique would eliminate trapping of any Hebetween the laminations during hot rolling. EB welding or TIG welding inHe whereby the He can be removed during hot rolling through a vent tubeare considered viable approaches. For example, laminates weresuccessfully EB welded and hot-rolled bonded when the laminates wereinserted into a dessicator and evacuated to a 10⁻⁶ torr (or better)vacuum within 10 to 15 minutes after the sanding and/or etching surfacepreparation described above. These laminates displayed complete bondingacross the width of the laminates, with no evidence of failures in thecoating induced during hot rolling. FIG. 7 shows a typical micrograph ofa bonded Zr-4/Er/Zr-4 laminate made by EB seal welding and then hot rollbonding an Er-coated substrate to an uncoated Zr-4 substrate.

CLOSURE

[0075] While a preferred embodiment of the present invention has beenshown and described, it will be apparent to those skilled in the artthat many changes and modifications may be made without departing fromthe invention in its broader aspects. The appended claims are thereforeintended to cover all such changes and modifications as fall within thetrue spirit and scope of the invention.

We claim:
 1. A laminated structure, comprising: a. a first metalsubstrate; and b. a thickness of an electrospark deposited coatingcomprising at least one rare earth, said coating metallurgically bondedto said first metal substrate and formed by the process of electrosparkdepositing a first material onto said first metal substrate from a firstelectrode comprising said at least one rare earth.
 2. The laminatedstructure as recited in claim 1, wherein said first metal substrate isselected from the group consisting of zirconium-based alloys, iron-basedalloys, and nickel-based alloys.
 3. The laminated structure as recitedin claim 1, wherein said at least one rare earth contains erbium.
 4. Thelaminated structure as recited in claim 1, wherein said first electrodeconsists essentially of a rare earth.
 5. The laminated structure asrecited in claim 4, wherein said rare earth is erbium.
 6. The laminatedstructure as recited in claim 1, wherein said thickness is up to 150 μm.7. The laminated structure as recited in claim 1, wherein said coatingis obtained in a single pass and has said thickness of up to 75 μm. 8.The laminated structure as recited in claim 1, wherein the process ofelectrospark deposition comprises the step of rotating said firstelectrode while rastering said first electrode across said first metalsubstrate while depositing said first material onto said first metalsubstrate from said first electrode through a plasma arc.
 9. Thelaminated structure as recited in claim 1, wherein said laminatedstructure is a component of a fissile material storage container.
 10. Alaminated structure, comprising: a. a first metal substrate; b. athickness of an electrospark deposited coating comprising at least onerare earth, said coating metallurgically bonded to said first metalsubstrate and formed by the process of electrospark depositing a firstmaterial onto said first metal substrate from a first electrodecomprising said at least one rare earth; and c. a second metal substratemetallurgically bonded to said coating.
 11. The laminated structure asrecited in claim 10, wherein said first and second metal substrates areselected from the group consisting of zirconium-based alloys, iron-basedalloys, and nickel-based alloys.
 12. The laminated structure as recitedin claim 11, wherein said first and second metal substrates are selectedfrom the group consisting of Zr—Sn, Zr—Nb, and Zr—Sn—Nb alloys.
 13. Thelaminated structure as recited in claim 12, wherein said first andsecond metal substrates are selected from the group consisting of UNSR60802, UNS R60804, and UNS R60901.
 14. The laminated structure asrecited in claim 10, wherein said at least one rare earth containserbium.
 15. The laminated structure as recited in claim 10, wherein saidfirst electrode consists essentially of a rare earth.
 16. The laminatedstructure as recited in claim 15, wherein said rare earth is erbium. 17.The laminated structure as recited in claim 10, wherein said secondmetal substrate is metallurgically bonded to said coating by the processselected from the group consisting of hot rolling, hot pressing, highdeformation rate processing, and combinations thereof.
 18. The laminatedstructure as recited in claim 10, wherein said laminated structure is acomponent of a nuclear fuel assembly.
 19. The laminated structure asrecited in claim 18, wherein said nuclear fuel assembly is used in anuclear reactor selected from the group consisting of boiling waterreactors and pressurized water reactors.
 20. The laminated structure asrecited in claim 19, wherein said component is a channel in a boilingwater reactor fuel assembly.
 21. The laminated structure as recited inclaim 10, wherein said laminated structure is a component of a fissilematerial storage container.
 22. A laminated structure, comprising: a. afirst metal substrate; b. a thickness of an electrospark depositedcoating comprising at least one rare earth and a second material, saidcoating metallurgically bonded to said first metal substrate and formedby the process of electrospark depositing a first material onto saidfirst metal substrate from a first electrode comprising said at leastone rare earth and then electrospark depositing said second materialonto said first material from a second electrode; and c. a second metalsubstrate metallurgically bonded to said coating.
 23. The laminatedstructure as recited in claim 22, wherein said first and second metalsubstrates are selected from the group consisting of zirconium-basedalloys, iron-based alloys, and nickel-based alloys.
 24. The laminatedstructure as recited in claim 23, wherein said first and second metalsubstrates are selected from the group consisting of Zr—Sn, Zr—Nb, andZr—Sn—Nb alloys.
 25. The laminated structure as recited in claim 24,wherein said first and second metal substrates are selected from thegroup consisting of UNS R60802, UNS R60804, and UNS R60901.
 26. Thelaminated structure as recited in claim 22, wherein said at least onerare earth contains erbium.
 27. The laminated structure as recited inclaim 22, wherein said first electrode consists essentially of a rareearth.
 28. The laminated structure as recited in claim 27, wherein saidrare earth is erbium.
 29. The laminated structure as recited in claim22, wherein said second electrode comprises an absorber.
 30. Thelaminated structure as recited in claim 22, wherein said secondelectrode comprises a base element of said second metal substrate. 31.The laminated structure as recited in claim 22, wherein said secondelectrode comprises at least one rare earth.
 32. The laminated structureas recited in claim 22, wherein said second metal substrate is bonded tosaid coating by the process selected from the group consisting of hotrolling, hot pressing, high deformation rate processing, andcombinations thereof.
 33. The laminated structure as recited in claim22, wherein said laminated structure is a component of a nuclear fuelassembly.
 34. The laminated structure as recited in claim 33, whereinsaid nuclear fuel assembly is used in a nuclear reactor selected fromthe group consisting of boiling water reactors and pressurized waterreactors.
 35. The laminated structure as recited in claim 34, whereinsaid component is a channel in a boiling water reactor fuel assembly.36. The laminated structure as recited in claim 22, wherein saidlaminated structure is a component of a fissile material storagecontainer.
 37. A method of making a laminated structure, comprising thesteps of: (a) providing a first metal substrate; and (b) metallurgicallybonding a thickness of a coating to said first metal substrate, saidcoating formed by the process of electrospark-depositing a firstmaterial onto said first metal substrate from a first electrodecomprising at least one rare earth.
 38. The method as recited in claim37, wherein said first metal substrate is selected from the groupconsisting of zirconium-based alloys, iron-based alloys, andnickel-based alloys.
 39. The method as recited in claim 37, wherein saidat least one rare earth contains erbium.
 40. The method as recited inclaim 37, wherein said first electrode consists essentially of a rareearth.
 41. The method as recited in claim 40, wherein said rare earth iserbium.
 42. The method as recited in claim 37, wherein said thickness isup to 150 μm.
 43. The method as recited in claim 37, wherein saidcoating is obtained in a single pass and has said thickness of up to 75μm.
 44. The method as recited in claim 37, wherein the process ofelectrospark depositing comprises the step of rotating said firstelectrode while rastering said first electrode across said first metalsubstrate while depositing said first material onto said first metalsubstrate from said first electrode through a plasma arc.
 45. A methodof making a laminated structure, comprising the steps of: (a) providinga first metal substrate; (b) metallurgically bonding a thickness of acoating to said first metal substrate, said coating formed by theprocess of electrospark-depositing a first material onto said firstmetal substrate from a first electrode comprising a rare earth; and (c)metallurgically bonding a second metal substrate to said coating. 46.The method as recited in claim 45, wherein said first and second metalsubstrates are selected from the group consisting of zirconium-basedalloys, iron-based alloys, and nickel-based alloys.
 47. The method asrecited in claim 46, wherein said first and second metal substrates areselected from the group consisting of Zr—Sn, Zr—Nb, and Zr—Sn—Nb alloys.48. The method as recited in claim 47, wherein said first and secondmetal substrates are selected from the group consisting of UNS R60802,UNS R60804, and UNS R60901.
 49. The method as recited in claim 45,wherein said at least one rare earth contains erbium.
 50. The method asrecited in claim 45, wherein said first electrode consists essentiallyof a rare earth.
 51. The method as recited in claim 50, wherein saidrare earth is erbium.
 52. The method as recited in claim 45, furthercomprising the step of electrospark-depositing a second material ontosaid first material from a second electrode comprising an absorber. 53.The method as recited in claim 45, further comprising the step ofelectrospark-depositing a second material onto said first material froma second electrode comprising a base element of said second metalsubstrate.
 54. The method as recited in claim 45, further comprising thestep of electrospark-depositing a second material onto said firstmaterial from a second electrode comprising at least one rare earth. 55.The method as recited in claim 45, wherein said metallurgical bonding isperformed by a process selected from the group consisting of hotrolling, hot pressing, high deformation rate processing, andcombinations thereof.
 56. The method as recited in claim 45, whereinsaid laminated structure is a component of a nuclear fuel assembly. 57.The method as recited in claim 56, wherein said nuclear fuel assembly isused in a nuclear reactor selected from the group consisting of boilingwater reactors and pressurized water reactors.
 58. The method as recitedin claim 57, wherein said component is a channel in a boiling waterreactor fuel assembly.
 59. The method as recited in claim 45, whereinsaid laminated structure is a component of a fissile material storagecontainer.
 60. The method as recited in claim 45, wherein the process ofelectrospark depositing comprises the step of rotating said firstelectrode while rastering said first electrode across said first metalsubstrate while depositing said first material onto said first metalsubstrate from said first electrode through a plasma arc.